Froth flotation of iron ores



(to waffe) ATTORNEY Patented Apr. l2, 1949 was FROTH FLOTATION F IRON DRES Earl Conrad Herkenhoif, Stamford, Conn., al-

signor to American Cyanamid Company, New York, N. Y., a corporation of Maine Application June 19;-I944, Serial No. 539.691 4 Claims. (Cl. 209-168) This invention relates to the beneficiation of iron ores by froth flotation. More particularly, the invention relates to a two-stage flotation process suitable for use on fines such as are found in the overflow from iron ore washer plants; in waste products from heavy media y separation processes and on those ores which must be ilnely ground in order to unlock the iron minerals from the gangue.

The present invention constitutes a modification of the multi-stage flotation process set forth in my copending application, Serial No. 468,524, flled December 10, 1942, now Patent 2,389,727 granted Nov. 27, 1945, of which the present application constitutes a continuationin-part.

Increasing amounts of the lower grade iron ores such as those with which the present invention is concerned, are coming into industrial importance because of the constantly decreasing amounts of available high grade ore. Most of these ores are too low in iron and too high in silica-bearing gangue to be suitable for use in blast furnaces. Consequently, if they are to be used they must be beneciated in some manner. Frequently, calcium carbonate and other alkaline earth carbonate minerals are also found in the ores. These, of themselves, are not particularly objectionable, in fact being to a certain extent desirable. In some cases, however, it may be necessary to remove aportion of these constituents in order to raise the iron content.

The principal problem, therefore, is one of reducing the impurities andvraising the iron content to as high a degree as possible. As was pointed out, this usually involves the removal of silica. The necessary degree of beneflciation lcan be accomplished in any one of several ways, depending on the ore. In some cases, the necessary rise in iron content may be made bymerely crushing and washing the ore. Where the iron minerals and the gangue are associated in such manner that this can not be done, but the mineral values can be released with moderately ilne crushing, heavy-media separation is particularly useful.

Much of the naturally occurring ore, however, requires ne grinding in ,order to enable separation of the objectionable gangue. After the necessary grinding is done, beneflciation by froth flotation is perhaps the most useful method of separating the gangue from the mineral values. In addition to the ores of this type, there are the wastes from the washing and the heavymedia processes mentioned above. Although too 2 low in iron content for ordinary use. because of the tremendous volumes involved 'they represent a very large amount of potentially useful iron mineral.

As pointed out above, one of the principal ob- ."ectionable constituents is usually a silica-bearing mineral of some type or other. From the point of view of susceptibility to froth flotation, this is particularly unfortunate since the iron minerals and these silica-bearing gangues are generally difficult to separate. Because of this separational difficulty, a flotation process to be successfully carried out requires careful handling, usually also accompanied by a high reagent consumption. All of these factors tend to increase the cost of processing. Yet iron ores, despite the fact that they must be handled in enormous quantities, are intrinsically cheap products and the margin of profit is small. Therefore beneflcation by froth flotation, if it is to be carried out, must be done cheaply, easily and emciently. In this respect, ordinary methods of beneflciating ores by froth flotation when applied to iron ores leave much to be desired.

Ordinarily, separation of mineral values from silica-bearing gangues by froth flotation takes one of two forms. Either the mineral values are floated from the silica by the use of an anionictype reagent or reagent combination, or the silica is floated from the mineral values by means of a cationic-type of reagent. In general, anionic flotation is the easiest and cheapest and is, therefore, used whenever possible. The usual procedures are old and well known in conjunction with many ores.

Usually, when applied to ordinary iron ores of the type with which the present invention is concerned, a straight anionic flotation does not work well. The iron minerals and the gangue tend to float together. yBy using sufficient care and the necessary large amount of reagents a benefication can be carried out whereby some 30 to 40% of the iron values can be recovered, but the grade of concentrate is usually too low. The grade can be improved somewhat at the expense of the recovery, but the net cost' is much higher than is practically desirable for the amount of mineral recovered at the corresponding.concentrations.

In such cases with other ores, the reverse procedure has been found useful, i. e., silica is floated from the mineral values with a cationic-type promoter. This process, when it can be properly used, gives good results. Howeven'it suffers from several inherent drawbacks which must be overcome. First of all,'the reagents are'relatively expensive, the unit cost being several times that of equal amounts of anionic-type reagents. They depend for competitive success on the fact that lf they can be used effectively they are highly selective, having great collecting power for silica and so can be used in smaller amounts.

Moreover, they must be very efficiently used and this involves a second difficulty, that of slimes. Cationic reagents are particularly sensitive to the presence of slimes, even a fractionA of a percent in the pulp being suiiicient to impair the efficiency of the reagent to a point where the reagent cost becomes prohibitive. Still another difficulty arises from the fact that cationic reagents are considerably less effective on coarse silica than on ne. If silica particles are present in a wide size range and a cationic reagent is used in sufficient quantities to float the coarsest silica particles its selectivity is greatly impaired.

In practical cationic operation, a balance must be made between the cost of preparing the ore such as the grinding, desliming, etc., the reagent cost, and the value of the minerals recovered. Unfortunately, in attempting to float silica from most low-grade iron ores this balance can not be satisfactorily accomplished. The cost of pretreating the ore to the optimum extent plus the reagent cost ordinarily raises the total above that which can be expended for the amount of ore recovered if the latter is to be sold in a competitive mai-het.

'There remains, therefore, a demand for a suitable beneiiciation process whereby the iron content of low grade ores, particularly the wastes from washer plants and the like, can be carried out at a cost which will permit the process to be used on a large scale. Itis the object of the present invention to establish a procedure of froth flotation by the use of which the desirable results ci cheaper and more effective concentration of the iron minerals may be obtained with these lowgrade starting materials.

In general, the desired object of the present invention is accomplished by a two-stage flotation. En the first stage, a major portion of the iron minerals together with a part of the gangue is floated away from the remainder of the ore by means of an anionic-type promoter. This concentrate is then treated with a suitable surfacemodifying agent adapted to overcome the effect of the anionic reagent without destroying the potential floatability of the silica. The conditioned ore is then subjected to flotation with a cationic-type reagent and the tailing from this operation constitutes the finished product, or iron concentrates.

'Ilhe procedure has a number of advantages. Lower cost reagents are used on the biggest bulk of materiial, whereby the latter is very appreciably reduced before the more expensive reagents need be employe-d. In this way the better features of both types of reagent are utilized to fullest advantage. A greater proportion of the iron minerals can be recovered in a good grade product than is ypractically possible by conventional singlestage operation. T-he present process produces an even greater saving than that of my previously identified copending appliction in that it eliminates the primary silica flotation. The present process, therefore, is n-ot only highly efficient as compared with older methods, but is also less expensive and readily adapted to use on a. large scale,

The process of the present invention will be more fully illustrated in conjunction with the accompanying drawing. The latter sets forth a. flow scheme incorporating the principal steps where-by the important advantages of the present invention are obtained.

The ore, as it is introduced into the process of the present invention is assumed to have been previously reduced to a suitable particle size. It may be deslimed if necessary. The desliming step, however, is optional, as shown in the drawing, and the ore may be directly conditioned with the anionic-type promoter. If a frother is desirable with the particular anionic collector, it is ordinarily added at the same time.

After being conditioned, the pulp is subjected to the first flotation step, whereby a concentrate rich in iron but containing a part of the gangue, is obtained. The tail-ing lis normally discarded as shown in the flow sheet. With some ores, this fraction may have a rather high iron assay, due to the presence of coarse, or middling particles of iron minerals. However, even in such cases, rit represents only a small `fraction of the total iron in the feed and may be discarded without further treatment. 1f so desired, the rougher concentrate produced in the anioni-c flotation may be given an optional cleaning, the taliling from which may be either discarded or recycled to the original conditioning step.

At this point, the rougher, or optionally the cleaner concentrate, is subjected to a step of primary importance iin the present process. In this operation it is conditioned with a depressant and/or dispersant. This treatment not only serves the several purposes of overcoming the effects 'of any residual anionc reagent from the first iiotation and dispersing the iron minerals b-ut is of denite assistance in the subsequent flotation of silica.

After being conditioned, the pulp is subjected to a silica flotation using a cationic reagent. The tailing from the cationic flotation comprises a. 'high-grade iron product. The silica concentrate may be either discarded or given an optional cleaning. in the latter case the cleaner concentrate is discarded and the cleaner tailing recycled to the dispersant conditioning step.

Since a principal purpose of the dispensant conditioning operation is to modify the flotation characteristics of the minerals, but the presence `of excess dispersants and depressants Iis objectionable during cationic flotation, the conditioned ore is ordinarily desllimed and Washed before adding the cationic reagent. As shown in the drawing, however, when such an excess is not present and the conditioning operation has not created sufficient slimes to interfere with the cationic reagent, this step may be by-passed. In fact, small amounts of certain reagents when present during the cationic flotation have a beneficial, selective depressant effect on the iron minerals.

It is an advantage of the present process that vdespite its being a two-stage flotation operation, it is in fact quite flexible and is readily adjusted for different ores. This may be noted, for example, in the several optional desliming and/or cleaning steps. In thlis regard, the cleaning is 4preferably done by flotation, but it is also possible to use gravity methods yof concentration such as tabling or ,vanning when such methods are advantageous.

, It is also an advantage that the reagents used may be varied considerably Without departing from the scope of the present invention. For example, in the anionic iiotation a wide range of suitable promoters is available. Excellent results 'can be obtained for example using an anionic ,promoter of the higher aliphatic fatty-acid type. Typically good results are obtained using a fattyacid promoter such as oleic acid. Other reagents which may be substituted therefor include, for example, the fish oil fatty-acids, cocoanut oil l fatty-acids, linseed oil fatty-acids, cottonseed oil fatty-acids, resin acids, napthenic acids, talloel and the like, sulfonates of these and like acids and sodium, potassium and ammonium soaps and emulsions thereof.

Excellent results are also obtained using as the anionic promoter, a reagent of the sulfonated hydrocarbon type. As in using fatty-acid reagents, the choice of a particular sulfonated-hydrocarbon reagent may be from a wide range of materials. By Way of example, both the oil-soluble, water-dispersible reagents of the mahogany acid or mahogany soap types, and the water-soluble green acid or green soap types. Such sulfonated products are commercially available in a number of different forms. However, as shown, for example, in U. S. Patent 2,331,049, their principal source is as by-products from the refining of petroleum lubricating oil fractions in the course of treatment with fuming sulfuric acids or sulfuric acids. When so produced, these byproducts are generally found to be salts of the sulfonated hydrocarbons, most commonly the sodium salt although other salts may be encountered. In some cases no attempt has been made to neutralize the acid product. Even after neutralization, free sulfonates and/or sulfates are often found.

In many cases, it is desirable to use a frother in conjunction with the anionic-type promoter. Any of the well-known frothers may be used. Among these are included, for example, pine oil, synthetic pine oil, cresylic acids, and the commerically available, aliphatic alcoholic frothers. These may be used alone, in admixture with each other, or with other forth modifying agents. In general, the fatty-acid type reagents require more careful use of frothing .agents whereas the sulfonated-hydrocarbon types often require little frother or none at all.

In my three-stage process, lime, or an equivalent alkaline earth hydroxide, was used alone, in amounts up to about 5.0 lbs/ton of original ore, as the iron mineral depressant. I'his Was found to leave the anionic concentrate in such a condition that the silica tended to float in the presence of a frother, although carrying with it a considerable proportion of iron. In my previous process this was turned to advantage to conduct a primary silica flotation without additional reagents, other than the possible use of a frother. Lime, or its equivalent, did not completely overcome the effect of the anionic reagents on the mineral surfaces.

According to the present process, it has been found that if the lime, or some other alkaline material such as soda ash or another alkalineearth-hydroxide is suitably supplemented, this primary silica notation is unnecessary. Such supplementary reagents are limited to those materials which selectively alter the surface conditions of the iron minerals, so that the effects of the anionic promoter are nullifie'd and they are not floated by the silica promoter in the subsequent flotation operation. At the same time, the supplementary reagents should not interfere with the silica flotation by wastefully consuming the cationic reagent or by acting as a silica depressant.

Surface-modifying agents found suitable for this purpose include for example, tannic acid, quebracho, dextrin (particularly yellow corn dextrin) and a number of phosphates such as trisodium phosphate, tetrasodium pyrophosphate, sodium acid pyrophosphate and the like. For the purposes of the present invention, these are all considered to be effective as dispersing agents, although their action also is probably depressant to a certain extent.

When sulfonated-hydrocarbon types of reagents are used in the initial or anionic flotation operation, quebracho is particularly effective, even With greatly reduced amounts of lime as compared to those required when using fatty-acid type reagents. In some instances, the use of lime even may be unnecessary and effective depression of the iron minerals may be accomplished by the use of the supplementary reagent alone. It should be noted, that anionic reagents of the sulfonated hydrocarbon type have been found to produce much better results when they are conditioned with flotation feed to which acid has been added.

Similarly, the silica concentration by flotation in the presence of a cationic promoter is not necessarily limited to the use of any particular reagent. For example, choice as to the cationic promoter used may be made from among the commercially available amines or amine salts such as lauryl and octadecyl amine and the like; quaternary onium" compounds such as cetyl trimethyl ammonium bromide and the like, many of which, alone or in combination, are commercially available for the purpose; or the polyalkylene-polyamine reaction products many of which are also commerically available. As in the anionic flotation, a small amount of frother often is desirable but not necessarily essential.

The process of the present invention will be described'in greater det-ail in conjunction with the following specific examples which are illustrative only and not meant by Way of limitation on the scope of the invention. Tons as used in the following examples refer to short tons. The percentage distribution of the iron and quantities of reagents employed are based on the deslimed feed to flotation. Desliming was done by hydraulic classification. The term "lime Ca(OH)2.

EXAMPLE 1 As illustrative of the practice and results obtained by straight anionic flotation a sample of overflow Waste principally composed of hematite and quartz from an iron ore washer plant, which presented beneciation problems typical of those with which the present invention is concerned, was made into a pulp containing about 20% solids, conditioned with 0.162 lb. per ton of a pine oil frother and 0.75 lb. per ton of oleic acid and subjected to froth flotation for 5 minutes in a Fagergren flotation machine. The concentrate therefrom was cleaned three times. The cleaned concentrate assayed 26.71% iron and contained 41,66% of the total iron contained in the feed. Since the feed contained 23.24% iron, the degree of concentration achieved is not appreciable. The standard method of anionic-type flotation, therefore, is not practical with this type of ore.

EXAMPLE 2 The procedure of Example 1 was repeated on the same ore with the exception that the ore was deslimed by hydraulic classification before being subjected to the original conditioning step. From a head assaying 23.84% iron, a concentrate asdesignates saying 27.95% iron and containing 37.70% oi the total iron fed was obtained. The results, while better than those of Example 1 are obviously not satisfactory from a commercial point of view.

EXAMPLE 3 .In order to obtain a. basis for comparison, another similar sample was given the following treatment. A pulp of the ore (60% solids) was ground for 12 minutes with 20 lbs per ton of sodium silicate and the ground ore deslimed by hydraulic classification. The deslimed ore was diluted to 20% solids, conditioned with 0.054 lb. per ton of pine oil, 1.0 1b. per ton of lime and 0.15 lb. per ton of octadecylamine and finally floated for three minutes. Promotion was unsatisfactory and the amount of cationic agent was increased. Finally using several times the original amount a concentrate representing 18% o the ore, containing 35% of the original iron and assaying 56.32% Fe was obtained. While the grade was satisfactory, the recovery is` not and the reagent consumption was too highfor industrial use.

The preceding examples show that when either anionic or cationic reagents are used alone in a single-stage flotation operation, the results produced are not particularly useful. The concentrates obtained are either too poor in grade or contain too small a fraction of the original iron or the reagent consumption is too high te be practical. By way of comparison a number of samples of different ores were then treated according to the process of the present invention using a variety of reagent combinations.

EXAMPLE 4 A sample of a, low-grade Minnesota iron ore was ground to about minus 20 mesh, deslimed hydraulically, conditioned for 2 minutes with 1.96 lbs. per ton of oleic acid and floated for two minutes, The concentrate was then conditioned for 2 minutes with 2.0 lbs. per ton of lime and 0.5 lb. Iper ton of sodium acid pyroph'osphate, deslimed and washed. The slimes removed were designated nes. A 5 minute flotation wasthen carried out using 0.11 lb. per ton of pipe oil and 0.25 lb. per ton of lauryl amine hydrochloride. Excellent grade and fair recovery were obtained as shown in Table I.

Another ore sample was conditioned for 2 minutes at 70% solids with 1 1b. per ton of sodium silicate and 2 lbs. per ton of saponied talloel. This pulp was diluted to about 22% solids and iloated for about 2 minutes, the resultant tailings being discarded. The concentrate was conditioned for minutes with 4 lbs. per ton of lime and ,/2 lb. per ton of Quebracho, After desliming the conditioned pulp, it was iloated for 4 minutes with 0.139 lb. per ton of pine oil and 0.15 1b. per ton of lauryl amine hydrochloride. Both good grade and good recovery were obtained. The results are' shown in Table II.

Table Il Distri- Assay Product Pvevrellt PerFCent Ifetol't EXAMPLE 6 ton of pine oil and 0.15 lb. per ton of laurylamine hydrochloride in the cationic stage. The results are shown in Table III,

T able I I I Distri- 100. 00 20. 20 100. 00 74. 24. 59 61. 16 25. 05 45.41 38. 84 0. 80 33. 25 0. 98 i). 09 21. 00 6. 70 Fe Conc 15.10 60. 43 31.16

The preceding'example illustrates the ability of a suitable depressant such as Quebracho when used in conjunction with a sulfonated-hydro- `carbon reagent to produce a concentrate of high grade, although recovery is poor. A minor part' of this loss is unavoidable because of the iron minerals carried away in the desliming operation'. However, the principal diiiculty is that the amonio-flotation recovery (rougher concentrate) is too low. This may be improved, as shown in the following example, when using sulfonated reagents by conditioning the ore with acid before the anionic iiotation, in accordance with the teachings of my copending joint application with R. B. Booth, Serial No. 481,906, iiled Api-i1 5, 1943, patented October 29, 1946, Patent No. 2,410,376. Enough alkaline material is used to produce an alkaline pH as well as to induce the desired surface conditions. When an acid-treated ore is treated with a sulfonated reagent, the alkaline material may be one of the same alkaline conditioning agents previously noted. However, for the purposes of overcoming the eiect of :the acid any strong alkali such as caustic soda, -potash and the like may be used. Similarly, excess acid may be reduced by using an alkaline-earth carbonate if so desired.

EXAMPLE 7 Another sample of low grade ore from the same source was conditioned for 2 minutes at about 67% solids with 2.50 lbs. per ton of sulfuric acid and 2.20 lbs. per ton of a mixture of oil-soluble, suifonated petroleum hydrocarbons, diluted to 20% solids and floated for three minutes with an additional 1.10 lbs. Iper ton of petroleum sulfonate. The concentrate was then conditioned with 2 lbs. per ton of Quebracho and 9 2 lbs. per ton ofl soda ash, deslimed and washed, and then given 'a 61/2 minute cationic notation with 0.108 lb. per ton of pine oil and 0.35 1b. per ton of laurylamine hydrochloride. An iron concentrate of good grade with very high recovery was obtained. The results are shown in Table IV.

When using acid conditions in the anionic flotation and the dis-persant-depressant conditioning step of the present invention, good results are obtained using other types of sulfonated fatty acids and sulfonated hydrocarbons as the anionic collectors. This is shown for example by the following examples.

EXAMPLE 8 A similar procedure to that of Example was carried out on a washer waste sample using 11/2 lbs. per ton of sulfuric acid and 1.5 lbs. per ton of sulfonated talloel in place of the sodium silicate and talloel soap of Example 5 in the anionic stage. The anionic concentrate was conditioned with 2 lbs. per ton of lime and 2 lbs. per ton of dextrln as the depressant and dispersant before being deslimed and was subjected to :a cationic silica flotation with 0.081 lb. per ton of frother and 0.15 lb. per ton of lauryl amine. A marked improvement in grade over that of Example 5 /is to be noted. The results are shown in Table V. It will be noted that even using a poorer feed, better concentration and better recovery were obtained than when using the straight talloel soap of Example 5.

Another washer waste sample was hydraulically deslimed and conditioned at about 65% solids for 2 minutes with 2.1 lbs. per ton of sulfuric acid, 1.6 lbs. per ton of sulfonated soyabean fatty acids and 4.0 lbs. per ton of fuel oil. The conditioned sample was then diluted to about 20% solids andan 'anionic concentrate collected for 2 minutes. This concentrate was then conditioned for minutes with 2.0 lbs. per ton each of lime and quebracho after which 2 lbs. per ton of sodium silicate was added and the conditioned concentrate given a secondary desliming. The cationic flotation was then carried out for 4 minu`tes with 0.11 lb. per ton of an alcoholic frother and 0.17 lb. per ton of laurylamine hydrochloride. The resultsare contained in Table VI.

Table VI Distri- Assayl.

Per Cent bution Product Weig Perrmt Per Cen't 100. 00 13. l5 100. 00 65. 83 2. 43 12. 11 5. 84 34. 70 15. 41 16. 77 17. l5 21.87 1l. 56 57. 51 50. 55

. EXAMPLE 10 Another sample of the same washer waste was treated as in Example 9 using 1.5 lbs. per ton of sulfuric acid, 2.0 lbs. per ton of water-soluble petroleum sulfonate and 0.5 lb. per ton of fuel oil as the anionic reagents; 1.5 lbs. per ton of quebracho, 2.0 lbs. per ton of soda ash as the depressant and dispersant reagents, and 0.11 lb. per ton of pine oil and 0.20 lb. per ton of laurylamine hydrochloride as the cationic flotation reagents. The results are shown in Table VII.

Table VII Distri- Assays Per Cent bution Product Weight PerFCent maroont Head 100.00 13.40 1001!) Rgh. Taxi.. 74. 94 1. 54 s 01 l 1.21 37.13 3.35 12.90 as. 77 31. 32 10.95 62.06 60.72

As is shown in Table VII the concentrate assayed 62.06% Fe. This in itself is an excellent grade but the concentrate is further notable in having a particularly low Insol content of 3.60%.

In the claims the term "oxidized iron ores" is used in its commonly accepted meaning to include not only iron oxide ores such as those containing magnetite, hematite, etc., but also hydroxides, carbonates, etc.

I claim:

1. A process of beneficiating oxidized-iron ores containing excessive amounts of acidic gangue which comprises the steps of forming an aqueous pulp of the ore of a size suitable for use as flotation feed; subjecting said pulp to froth flotation in the presence of an anionic-type promoter, selected from the group consisting of the higher aliphatic fatty acids, resin acids, naphthenic acids, talloel, sulfonates of such acids, sodium, potassium and ammonium soaps and emulsions thereof and sulfonated petroleum hydrocarbons of the oil-soluble, Water-dispersible mahogany acid and mahogany soap types and the Watersoluble green acid and green soap types obtained vin the acid treatment in refining lubricating oils;

collecting the resultant iron-minerals-rich froth concentrate; conditioning an aqueous pulp of the iron concentrate with (a) material, selected from the group consisting of the alkali and alkalineearth metal hydroxides and carbonates, in amount sufficient to overcome the tendency of the iron minerals as activated by the anionic promoter to float and to maintain an alkaline pH; and (b) with a surface-modifying agent, selected from the group consisting of quebracho, tannic acid, and dextrin and in suilcient amount to prevent flotation of oxidized-iron minerals in the presence of a cationic-type promoter for acidic gangue; 'subjecting the conditioned concentrate to froth flotation in the presence of a cationictype promoter selected from the group consisting K bracho.

li of the long-chain aliphatic amines containing 12-18 carbon atoms, Quaternary onium com- ,pounds and the polyalkylene-polyamine reaction products type used in amount sufficient to remove the excess acidic sangue and collecting the tailing which is rich in iron and low in gangue.

2. A process according,r to claim 1 in which the pulp of the ore is conditioned with a strong acid prior to the anionic otation.

3. A process according to claim l in which the surface-mocifying agent comprises que- 4. A process according to claim 1 in which the surface-modifying agent comprises dextrin.

mmm Corman HERKENHOFF. 15

REFERENCES CITED The following references are of record in the flle of this patent: 

